As the pharmaceutical industry advances, numerous drugs are available to address a variety of medical conditions. Individuals may increasingly be prescribed numerous drugs by multiple practitioners. Negative interactions between different drugs are a risk to patients that has been known for many years. Publications of known interactions and software tools that monitor medication lists assist medical care providers in preventing patients from receiving incompatible drug combinations. More recently, genetic research has shown that medications may react differently in patients with different genetic variants. It is estimated that 20-90% of an individual's variation to drug response is based on genetics. (Kang J. Testing Pathway-Dose Interaction in Clinical Studies. 2013 Joint Statistical Meeting—American Statistical Association.) Within the top 200 selling prescription drugs, 59% of the 27 most frequently cited in adverse reactions are metabolized by at least one enzyme known to have gene variants that code for reduced-functioning or non-functioning proteins. (Phillips K A, Veenstra D L, Oren E, Lee J K, Sadee W. Potential Role of Pharmacogenomics in Reducing Adverse Drug Reactions: A Systematic Review. JAMA. 2001; 286(18):2270-2279.)
Patients with different drug metabolizing enzyme phenotypes based on their genotype may metabolize drugs at different rates. More than 75% of the population has genetic variations that decrease or increase the availability or characteristics of cytochrome enzymes used in drug metabolism. For example, three cytochrome P450 enzymes, CYP2D6, CYP2C9, and CYP2C19 process more than 50% of all medications routinely prescribed. If a patient has a genetic variation affecting the availability of one of these enzymes and is prescribed a drug that relies upon one of those enzymes, an adverse drug event of overdose toxicity or treatment failure may occur. For example, if a patient has lower CYP2C9 enzyme levels, the patient may metabolize warfarin more slowly. This could lead to the patient suffering symptoms of overdose toxicity at a dosage within the normally prescribed therapeutic range. This may require adjusting the dose of the medication or choosing a different medication for the patient to prevent an adverse drug event.
Although increasing amounts of information on pharmacogenetic effects is available, it is still cost prohibitive to obtain genotype information for every individual patient. Often, healthcare providers have limited, if any, information about the genotype of their patients.
Moreover, testing to identify particular patient genotype information by DNA testing—may be costly. Healthcare providers are generally without tools which allow them to easily assess when, and in what patient populations, the costs of obtaining genotype information may outweigh potential adverse outcomes.